import pygame

from pygame.sprite import Sprite

class Ship(Sprite):
    """管理飞船的类"""

    def __init__(self,ai_game):
        """初始化飞船，并初始化飞船的位置"""
        super().__init__()
        self.screen = ai_game.screen
        self.settings = ai_game.settings
        self.screen_rect = ai_game.screen.get_rect()


        #加载飞船图像，并获取其外接矩形
        self.image = pygame.image.load('images/ship.bmp')
        self.rect = self.image.get_rect()

        #对于每艘新飞船，都放在底部中央
        self.rect.midbottom = self.screen_rect.midbottom

        #在飞船的属性x中存储小数值
        self.x = float(self.rect.x)

        #移动标志
        self.moving_right = False
        self.moving_left = False


    def update(self):
        """根据移动标志调整飞机位置"""
        #更新飞船而不是rect对象的x值
        if self.moving_right and self.rect.right < self.screen_rect.right:
            #更新前self.rect.x += 1,更新后如下
            self.x += self.settings.ship_speed
        if self.moving_left and self.rect.left > 0:
            self.x -= self.settings.ship_speed

        #根据self.x更新rect对象
        self.rect.x = self.x


    def blitme(self):
        """在指定位置绘制飞船"""
        self.screen.blit(self.image,self.rect)

    def center_ship(self):
        """让飞船在屏幕底端居中"""
        self.rect.midbottom = self.screen_rect.midbottom
        self.x = float(self.rect.x)